Laser radiation is increasingly being used in crime scene investigation for detecting trace evidence such as fingerprints or bodily fluid residue. Generally a surface being investigated for such trace evidence is irradiated by laser radiation having a wavelength that is absorbed by trace material being sought and will stimulate fluorescence or luminescence characteristic of the material. The laser-radiation-irradiated surface is observed, usually in a darkened environment, through an optical filter that blocks the stimulating radiation and transmits the stimulated luminescence such that trace evidence present on the irradiated surface appears bright against a dark background. The surface may be treated with a dye that can be preferentially absorbed by certain kinds of trace materials and has a brighter luminescence than the material. This is preferred in particular for fingerprint detection.
In a practical apparatus the wavelength of the laser radiation is selected to be able to stimulate fluorescence in a range of trace materials. One disadvantage of this is that not all materials in the range may be equally detectable. Another disadvantage is that, fingerprint detection aside, it may not be clear what trace materials are being detected.
There is a need to increase that range of materials simultaneously detectable by laser stimulated fluorescence. It would be advantageous to be able to identify in situ trace materials that are detected.